Geometric Adaptation Research Articles

Preoperative Planning for Physician-Modified Endografts Using a Three-Dimensional Printer.

The medical uses of three-dimensional (3D) printing are evolving at a rapid pace. The current roles and the future outlooks of this technology for physician-modified endovascular graft (PMEG) in patients with juxtarenal aneurysm are discussed. Fenestrations of PMEG are designed taking into account the geometry of the stent graft. Designing of such stent grafts is extremely complicated, especially when PMEG is planned for the angulated portion of the aorta. A 3D model enables the designing of branch fenestrations, with consideration for the geometrical adaptation of the stent graft in a complex aortic anatomy. With the aid of 3D-printing technology, patients with juxtarenal aortic pathologies can be treated using fenestrated stent grafts, preserving the vital organ circulation and securing a robust length of proximal sealing zone.

Grinding force modelling for ductile-brittle transition in laser macro-micro-structured grinding of zirconia ceramics

Laser ablation accomplishes high geometrical adaptability by the use of pulsing lasers and permits the manufacture of macro-micro-structures. In this paper, a systematic approach with a laser structuring technology was devised and utilized to generate macro-micro-structured patterns on the diamond wheel surface. An experiment on zirconia ceramic grinding was performed by the macro-micro-structured wheel. The grinding force and the surface morphology were investigated. The forming mechanism of the three grinding stages was analyzed, including ductile-stage grinding, ductile-to-brittle-transition-stage grinding and brittle-stage grinding. A theoretical grinding force model was presented by taking into account the three grinding stages in laser macro-micro-structured grinding (LMMSG). In addition, the mean grinding depths were defined in grinding force modelling for the ductile area, the ductile-to-brittle-transition area and the brittle area, separately. The amount of effective diamond grains was proposed for the final grinding force model. The model revealed the connection between the grinding force and the grinding parameters. Finally, the model was verified by experiments, and the experimental results were coincided with model predictions. It was obvious that the theoretical grinding force model may be available to predict the grinding force of zirconia ceramics under the LMMSG condition. Meanwhile, the influence between the grinding parameters and the surface morphology were discussed. The experimental results verify that the three grinding stages were existed and the theoretical model was proved to be reliable.

Researching of commonalities and differences in cold forging of spur and helical gears

Modern automobiles are equipped with a large number of gear transmissions. In the powertrain, for example, they are used as multi-stage manual transmissions and in the interior for mirror and seat adjustment. Machining manufacturing processes—like gear hobbing and shaping—represent the state of the art in gear manufacturing due to high manufacturing accuracy and flexible machining possibilities. With regard to economic, ecological and technical aspects, cold forging offers a promising production technology. In conventional transverse and forward extrusion processes, the ejection process is a challenge due to high forces and a negative influence on the gearing accuracy. One variant of forward extrusion is the so-called “Samanta” process, whereby an additional ejection step is avoidable by sequential forming of the gears. For the establishment of this process in industry, the increase of the achievable gearing accuracy and the achievable tool life is of major relevance. Thus, a deeper process understanding as well as knowledge about the influences on the process results is beneficial. In this context, the aim of this research work is to produce spur and helical gears by the “Samanta”-process. In addition to the resulting component properties, the characteristics of the process are determined. On this basis, commonalities and differences in cold forging of spur and helical gears are investigated to gain a principle process understanding. These findings are also used to derive possible approaches for improving component and process properties in future research work. The results reveal that cold forging of spur and helical gears by the “Samanta”-process results in characteristic properties and specific challenges within the gear types. Furthermore, a geometric adaptation in the gearing area of the used die promises enormous potential for a positive influence on the process results for both types of gearing.

Flexible tooling for impulse forming

Abstract With impulse forming technologies like electrohydraulic and electromagnetic forming, the punch in a stamping process is replaced by an impulse that acts in a short period and provides high strain rates of over 1000 s-1. Beneath the advantages which are accompanied with high speed forming the used dies and tools have to withstand mainly dynamic loads. This enables the realization of new concepts to increase flexibility in tooling for impulse forming. The flexibility covers different aspects like intrinsic geometrical adaptability of the punch, reduced demand for mechanical stiffness, rapid manufacturing of the dies due to the usability of alternative tool materials, modular dies and the opportunity of consecutive or parallel process combinations. These aspects of flexible tooling are illustrated by examples in different size scales for sheet metal, tube and bulk forming. The proposed techniques allow cold forming of small series or even single parts more cost and time efficiently.

Developing an Extended IFC Data Schema and Mesh Generation Framework for Finite Element Modeling

Mesh generation plays an important role in determining the result quality of finite element modeling and structural analysis. Building information modeling provides the geometry and semantic information of a building, which can be utilized to support an efficient mesh generation. In this paper, a method based on BRep entity transformation is proposed to realize the finite element analysis using the geometric model in the IFC standard. The h‐p version of the finite element analysis method can effectively deal with the refined expression of the model of bending complex components. By meshing the connection model, it is suggested to adopt the method of scanning to generate hexahedron, which improves the geometric adaptability of the mesh model and the quality and efficiency of mesh generation. Based on the extension and expression of IFC information, the effective finite element structure information is extracted and extended into the IFC standard mode. The information is analyzed, and finally the visualization of finite element analysis in the building model can be realized.

Online adaption approaches for intensity modulated proton therapy for head and neck patients based on cone beam CTs and Monte Carlo simulations

To develop an online plan adaptation algorithm for intensity modulated proton therapy (IMPT) based on fast Monte Carlo dose calculation and cone beam CT (CBCT) imaging.A cohort of ten head and neck cancer patients with an average of six CBCT scans were studied. To adapt the treatment plan to the new patient geometry, contours were propagated to the CBCTs with a vector field (VF) calculated with deformable image registration between the CT and the CBCTs. Within the adaptive planning algorithm, beamlets were shifted following the VF at their distal falloff and raytraced in the CBCT to adjust their energies, creating a geometrically adapted plan. Four geometric adaptation modes were studied: unconstrained geometric shifts (Free), isocenter shift (Iso), a range shifter (RS), or isocenter shift and range shifter (Iso-RS). After evaluation of the geometrical adaptation, the weights of a selected subset of beamlets were automatically tuned using MC-generated influence matrices to fulfill the original plan requirements. All beamlet calculations were done with a fast Monte Carlo running on a GPU (graphics processing unit).Geometrical adaptation alone only worked with small anatomy changes. The weight-tuned adaptation worked for every fraction, with the Free and Iso modes performing similarly and being superior than the two range shifters modes. The mean V95 and V107 were 99.4 ± 0.9 and 6.4% ± 4.7% in the Free mode with weight tuning. The calculation time per fraction was ~5 min, but further task parallelization could reduce it to ~1–2 min for delivery adaptation right after patient setup.An online adaptation algorithm was developed that significantly improved the treatment quality for inter-fractional geometry changes. Clinical implementation of the algorithm would allow delivery adaptation right before treatment and thus allow planning margin reductions for IMPT.

Construction of polyhedral finite element meshes based upon marching cube algorithm

Hexahedral meshes that exhibit the superiority in terms of solution accuracy and convergence rate are preferred to other types of meshes in the finite element analysis. However, the construction of the hexahedral meshes for complex geometries is still considered troublesome due to their poor geometric adaptability. This paper presents an efficient grid-based scheme to automatically generate polyhedral meshes including the hexahedral elements, and thus to provide hexahedral-dominant meshes for three-dimensional geometry with complex shapes. On the basis of the marching cube algorithm with a background grid composed of a regular arrangement of cubes, surface topologies for the background cubes are defined to represent the three-dimensional boundaries of a given domain. Then, in order to generate a three-dimensional finite element mesh, the surface topologies of the marching cube algorithm are systematically expanded to polyhedral volume topologies. Meanwhile, a topology ambiguity problem inherent in the marching cube algorithm is effectively resolved to generate an appropriate polyhedral mesh even for an arbitrary complex geometry. Several examples including biostructure modeling demonstrate that the proposed mesh generation scheme can easily discretize complex three-dimensional domains with hexahedral-dominant meshes, which are composed of the polyhedral elements near the domain boundaries and the hexahedral elements that come from the background cubes inside the domains. Furthermore, to show the applicability and effectiveness of polyhedral meshes in the finite element analysis, some structural analyses are performed using the smoothed finite element method that can be straightforwardly adapted to polyhedral elements of arbitrary shape.

Diseño de una cubierta hiperbólica plegable tensada

RESUMEN
 Se procesa la adecuación geométrica descriptiva de un sistema transformable, y cómo simular la modelación de sus partes por medio de un software que ayuda a concebir las interpretaciones de diseño de una geometrización hiperbólica. La modelación a escala apoya mucho a interpretar los movimientos de un sistema transformable, para generar un sistema flexible, el que se propone una piel de tenso estructura que ayuda a crear una estructura fácil de transportar y construir en sitios variables. Por esto, la investigación se centró en procesar los detalles experimentales y diseñarlos en 3D, para verificar la pertinencia de diseño de uniones articuladas.

Application of system of geometrical and technological adaptation of process laser-arc hybrid welding for production in the minimum tolerances of hull designs of means of marine engineering

The shipbuilding industry requires high-performance production technologies for the heavy gauges. One of the key tasks in advancing of hull production technology is minimization of welding deformations and simultaneous provision of high production performance. An arc augmented laser-arc welding technology which provides higher productivity, improvement of production effectiveness and reliable quality of welded joints is the most promising technology for this task. There are several limitations of industrial application of laser and hybrid laser arc welding concerned with sensitivity of laser technologies to the assembling quality of details before welding. Presented work describes designed algorithm and system of geometrical and technological adaptation increasing efficiency of laser-arc hybrid welding for production in the minimum tolerances of hull designs of means of marine engineering.

The HyTeG finite-element software framework for scalable multigrid solvers

ABSTRACTIn this article, a new generic higher-order finite-element framework for massively parallel simulations is presented. The modular software architecture is carefully designed to exploit the resources of modern and future supercomputers. Combining an unstructured topology with structured grid refinement facilitates high geometric adaptability and matrix-free multigrid implementations with excellent performance. Different abstraction levels and fully distributed data structures additionally ensure high flexibility, extensibility, and scalability. The software concepts support sophisticated load balancing and flexibly combining finite-element spaces. Example scenarios with coupled systems of partial differential equations show the applicability of the concepts to performing geophysical simulations.

A Weak Formulation for Isogeometric Analysis of Vibro-Acoustic Systems with Non-Conforming Interfaces

This paper develops a weak formulation for steady-state dynamic analysis of vibro-acoustic systems in the isogeometric framework. The Non-Uniform Rational B-Splines (NURBS) polynomials are used as basis functions for both geometrical transformation and numerical approximation. Starting from a NURBS-based geometrical projection that transforms a general, complex domain to a regular, spectral domain, an energy-based numerical model is then built, in which NURBS are again used as wholly admissible functions to approximate the structural displacement and the acoustic sound pressure. This process eventually leads to a set of discretized equations, based on which the system’s dynamic properties can be obtained. Besides better accuracy and excellent geometrical adaptivity, the main merit of the proposed method lies in its element-free feature of system modeling, which provides a natural solution for structural-acoustic coupling with non-conforming interfaces. This non-conformity results from either non-matching control points along the boundary or distinct polynomial orders used by adjacent patches, which is inevitable for a vibro-acoustic system given its multi-physics nature. The reliability of the proposed method is validated by a benchmark example. Its accuracy and efficiency are further investigated through a more general, car-like vibro-acoustic system.

The surrounding cell method based on the S-FEM for analysis of FSI problems dealing with an immersed solid

In this paper, a numerical method based on the cell-based smoothed finite element method is proposed to analyze three-dimensional fluid–solid interaction problems. Applying the gradient smoothing technique to the fluid and solid domain, the fully-coupled FSI formulation is achieved, and the analysis is performed by means of polyhedral smoothed finite elements. The element shape function based on the linear point interpolation leads to simple element formulation and a good geometric adaptability. Due to the properties of the smoothed finite element method, it is possible to connect non-matching meshes by polyhedral elements and provide seamless connection without overlapping or gap satisfying the interfacial conditions of continuity and force equilibrium, which is verified through the patch test. In addition, a treatment for dealing with moving boundaries in FSI problems with an immersed solid is proposed in the framework of local remeshing. By adopting a surrounding cell around a submerged solid, ill-shaped meshes occurring due to solid motion is reconstructed effectively. The effectiveness of the proposed scheme is illustrated through numerical examples in comparison with some previous works.

Adaptation of cardiovascular system stent implants.

Time-consuming design and manufacturing processes are a serious disadvantage when adapting human cardiovascular implants as they cause unacceptable delays after the decision to intervene surgically has been made. An ideal cardiovascular implant should have a broad range of characteristics such as strength, viscoelasticity and blood compatibility. The present research proposes the sequence of the geometrical adaptation procedures and presents their results. The adaptation starts from the identification of a person's current health status while performing abdominal aortic aneurysm (AAA) imaging, which is a point of departure for the mathematical model of a cardiovascular implant. The computerized tomography scan shows the patient-specific geometry parameters of AAA and helps to create a model using COMSOL Multiphysics software. The initial parameters for flow simulation are taken from the results of a patient survey. The simulation results allow choosing the available shape of an implant which ensures a non-turbulent flow. These parameters are essential for the design and manufacturing of an implant prototype which should be tested experimentally for the assurance that the mathematical model is adequate to a physical one. The article gives a focused description of competences and means that are necessary to achieve the shortest possible preparation of the adapted cardiovascular implant for the surgery.

Load Adaptation of Lamellipodial Actin Networks

Actin filaments polymerizing against membranes power endocytosis, vesicular traffic, and cell motility. Invitro reconstitution studies suggest that the structure and the dynamics of actin networks respond tomechanical forces. We demonstrate that lamellipodial actin of migrating cells responds to mechanical load when membrane tension is modulated. Inasteady state, migrating cell filaments assume the canonical dendritic geometry, defined byArp2/3-generated 70° branch points. Increased tension triggers a dense network with a broadened range ofangles, whereas decreased tension causes a shift to a sparse configuration dominated by filaments growing perpendicularly to the plasma membrane. We show that these responses emerge from the geometry of branched actin: when load per filament decreases, elongation speed increases and perpendicular filaments gradually outcompete others because they polymerize the shortest distance to the membrane, where they are protected from capping. This network-intrinsic geometrical adaptation mechanism tunes protrusive force in response to mechanical load.

Polyhedral elements using an edge-based smoothed finite element method for nonlinear elastic deformations of compressible and nearly incompressible materials

Polyhedral elements with an arbitrary number of nodes or non-planar faces, obtained with an edge-based smoothed finite element method, retain good geometric adaptability and accuracy in solution. This work is intended to extend the polyhedral elements to nonlinear elastic analysis with finite deformations. In order to overcome the volumetric locking problem, a smoothing domain-based selective smoothed finite element method scheme and a three-field-mixed cell-based smoothed finite element method with nodal cells were developed. Using several numerical examples, their performance and the accuracy of their solutions were examined, and their effectiveness for practical applications was demonstrated as well.

Application of the virtual density theory in fast reactor analysis based on the neutron transport calculation

The geometry distortion introduces one of the most important reactivity feedbacks in the fast reactor. To evaluate the reactivity caused by the geometry distortion, this paper presents a new approach applied in the steady-state fast reactor code SARAX. This approach is based on the discrete ordinates nodal method, first-order perturbation approximation and virtual density theory. In this way, the virtual material density is changed instead of changing the geometry in modeling the distortion. Compared with other methods to get geometry distortion reactivity, this method has better geometric adaptability and better efficiency in the multi-case evaluation. A series of verification are carried on, including the uniform expansion, the non-uniform expansion and the local geometry distortion. The results show that the virtual density method has good accuracy and efficiency in evaluating the geometry distortion reactivity.

Thermodynamic analysis of recuperative gas turbines and aero engines

In the current work, the thermodynamic cycle of a conventional recuperative aero engine, in which a heat exchanger is placed after the power turbine, is compared with the thermodynamic cycles of two non-conventional recuperative aero engine configurations. For each configuration, different heat exchanger designs were used, all having the same core arrangement as the heat exchanger in the conventional recuperation aero engine which was designed by MTU aero engines AG and has been initially used in the first concept of the Intercooled Recuperative Aero engine of MTU. The core of the heat exchangers is specially designed to enhance heat transfer and minimize pressure losses when used as a recuperator in aero engines. Regarding the non-conventional cycle configurations, the first one is referred to as ‘alternative recuperative’ cycle, where a heat exchanger is placed between the high pressure and the power turbine, while the second one is referred to as ‘staged heat recovery’ where two heat exchangers are employed, one between the high and power turbines and the second one at the exhaust, downstream the power turbine. The comparison is based on the efficiencies and the thrust specific fuel consumption of each thermodynamic cycle. The performance characteristics of the heat exchangers were defined from previous experimental measurements and computational fluid dynamics. For all the examined configurations, the aero engine geometrical constrains were taken into consideration, especially for the alternative recuperative cycle. The results of the study showed that the alternative recuperative and the staged heat recovery cycles were more efficient than the conventional recuperative cycle for a specific range of pressure ratios and heat exchangers characteristics. These cycles combined with appropriate geometrical adaptations and with advanced, temperature resistant ceramics, alloys and other materials have the potential to further optimize the waste heat management exploitation in aero engines.

Mechanosensation across borders: fibroblasts inside a macroporous scaffold sense and respond to the mechanical environment beyond the scaffold walls.

In tissue defects, cells face distinct mechanical boundary conditions, but how this influences early stages of tissue regeneration remains largely unknown. Biomaterials are used to fill defects but also to provide specific mechanical or geometrical signals. However, they might at the same time shield mechanical information from surrounding tissues that is relevant for tissue functionalisation. This study investigated how fibroblasts in a soft macroporous biomaterial scaffold respond to distinct mechanical environments while they form microtissues. Different boundary stiffnesses counteracting scaffold contraction were provided via a newly developed in vitro setup. Online monitoring over 14days revealed 3.0 times lower microtissue contraction but 1.6 times higher contraction force for high vs. low stiffness. This difference was significant already after 48h, a very early stage of microtissue growth. The microtissue's mechanical and geometrical adaptation indicated a collective cellular behaviour and mechanical communication across scaffold pore walls. Surprisingly, the stiffness of the environment influenced cell behaviour even inside macroporous scaffolds where direct cell-cell contacts are hindered. Mechanical communication between cells via traction forces is essential for tissue adaptation to the environment and should not be blocked by rigid biomaterials. Copyright © 2017 John Wiley & Sons, Ltd.

A fast and automatic full-potential finite volume solver on Cartesian grids for unconventional configurations

To meet the requirements of fast and automatic computation of subsonic and transonic aerodynamics in aircraft conceptual design, a novel finite volume solver for full potential flows on adaptive Cartesian grids is developed in this paper. Cartesian grids with geometric adaptation are firstly generated automatically with boundary cells processed by cell-cutting and cell-merging algorithms. The nonlinear full potential equation is discretized by a finite volume scheme on these Cartesian grids and iteratively solved in an implicit fashion with a generalized minimum residual (GMRES) algorithm. During computation, solution-based mesh adaptation is also applied so as to capture flow features more accurately. An improved ghost-cell method is proposed to implement the non-penetration wall boundary condition where the velocity-potential of a ghost cell is modified by an analytic method instead. According to the characteristics of the Cartesian grids, the Kutta condition is applied by specially computing the gradients on Kutta-faces without directly assigning the potential jump to cells adjacent wake faces, which can significantly improve the solution converging speed. The feasibility and accuracy of the proposed method are validated by several typical cases of sub/transonic flows around an ONERA M6 wing, a DLR-F4 wing-body, and an unconventional figuration of a blended wing body (BWB). The validation cases demonstrate a fast convergence with fully automatic grid treatment and computation, and the results suggest its capacity in application for aircraft conceptual design.

Abstracts of the SA Heart Congress 2010

Introduction: The pathophysiology of left ventricular (LV) remodelling in patients with hypertension (HT) is unclear. Aim: To evaluate the impact of four different types of geometric adaptations to hypertension on left ventricular ejection fraction (LVEF). Methods: A prospective single-centre study of 175 Black African patients (55% female, age = 53.1 ± 10.1 years) with moderate-to-severe HT was performed. HT was defined as systolic or diastolic daytime ambulatory BP (ABPM) >140mmHg or 95mmHg respectively. Echocardiography was performed using a HP 1 500 machine connected to 2.5 MHZ transducer. LV dimensions (LVEDD, LVESD, LVEF) were measured using standard American Society of Echocardiography definitions. Comparisons between the four geometric patterns were analysed using the Kruskal-Wallis test. Conclusion: Patients with eccentric LVH have the lowest systolic performance as measured by LVEF. These results suggest that patients with eccentric LVH need more aggressive therapy for heart failure.